Self-propelled powder aerosol system



3,081,223 SELF-PROPELLED PUWDER AEROSGL SYSTEM Paul E. Gunning, Kenmore, and Donald R. Rink, Buifalo,

N.Y., assignors to Union Carbide Corporation, a corporation of New York No Drawing. Filed July 19, 1961, Ser. No. 125,071 7 Claims. (Cl. 16739) The present invention relates to a self-propelled powder aerosol system for use in a pressurized container adapted to deliver a dry spray of the powder in a substantially liquid-free stream of a propelling gas.

Aerosol-type containers have achieved a great deal of popularity as means for dispensing a fluidized product. For example, such products as insecticides, agricultural compositions, anti-perspirants, body powders and medicant powders are widely used in such a manner. The possible applications to which an aerosol system might be applied are virtually numberless. Normally, the most common systems utilize a propellent gas in mixture with a liquid. When the dispensed material leaves the aerosol container in liquid form, there is no problem encountered. Such a container charge usually takes the form or" a mixture made up of the dispersed liquid, and a suitable propellent. Similarly, when a powder is to be dispensed, the slurry type of mixture may be employed but only to a limited extent.

operationally, dispensing a dry powder in the one of above-noted manners involves several problems. Primary among such problems is clogging of the container valve. Also, agglomerating of the powder both in the container and in the valve sections tend to decrease the value of this dispensing means. Furthermore, there are instances when even minute particles of the propellent in liquid phase would be undesirable in the dispensed stream. Notably in the treatment of foods or open wounds, with an aerosol dust the presence of liquid would be prohibitive.

The industry has attempted in many ways to overcome these problems and devise means for satisfactorily delivering a powder. Among these means is closer control of the powder particles. A further device resorted to by the industry is to provide especially constructed containers, or aerosol bombs as they are frequently referred to, in which the powder material and the liquid propellent are separately stored prior to activation of the control valve.

It is readily appreciated that since much of the value of an aerosol system lies in the expendability of the container, any factor which increases the cost of this item is economically impractical.

Therefore, it is a main object of the invention to provide a self-propelled aerosol system for use in a pressurized container which system contains a minor portion of a liquefiable gas propellent, and a major portion of a powdered material which is to be delivered from the container in a dry condition in a substantially liquid-free gaseous stream.

A further object is to provide a self-propelled aerosol system for use in a pressurized container which system comprises a liquefied fluorocarbon propellent gas, and a powdered composition consisting of an active powder to be delivered from the container, and a gas-sorent carrier, the latter holding at least a portion of the propellent gas in the liquid state.

A still further objective is to provide a self-propelled 3,81,223 Patented Mar. 12, 1963 aerosol powder of the type described in which the active powder comprises the major portion of the composition, said powder, containing the liquefied propellent gas in a sorbed condition. It is also an objective to provide an aerosol system of the type described, exhibiting a high degree of efiiciency in terms of the amount of powder dispensed relative to the amount of propellent gas employed.

In brief, the self-propelled aerosol system contemplated by the present invention comprises a three-phase system including a vapor phase and a homogeneous, free-flowing powdered composition, the latter containing a vaporizable propellent. The powder composition which constitutes a major portion of the system, provides the supporting phase. This powder composition is made up of particles of the material to be dispensed from the container, and means for holding the liquefied propellent at the vaporization pressure of said propellent at the ambient temperature of the pressurized system.

The present self-propelled powder systems are readily distinguishable from and in many ways advantageous over the previously mentioned slurry systems. In the latter, the liquid propellent constitutes the supporting phase whereas in a powder system, the powder is the supporting phase. As presently referred to and for the purpose of clarity in the subsequent description, the system is characterized by the fact that the ingredient defining the supporting phase of the composition may be added to without changing or causing an inversion in the overall system from one phase to another. For example, a phase inversion is experienced when by virtue of the addition of a certain ingredient the system changes from the powder to the slurry condition, or vice versa.

It is understood that the term powder or active powder as employed in the description includes a wide Variety of materials. For instance, powder compositions are normally compounded of several ingredients each of which serve a particular purpose, such as bulking agents, flavorants, odorants, surfactants, antiseptics and the like.

Whlie the instant aerosol system may be modified to assume a number of embodiments, basically we provide a self-propelled powder which may be charged into an aerosol container to deliver a spray of the powder in a liquid-free stream of the vaporized propellent. It has been found that a system is highly economical in terms of amount of active material dispensed relative to the amount of propellent employed. In one instance, for example, it was found that virtually the entire charge of an aerosol container was satisfactorily dispensed when the charge consisted of about percent by weight of active powder to 10 percent by weight of liquid propellent.

Ideally, the powder dispensed would be the active ingredient of the mixture; this however is true only if said active ingredient is capable of holding in the sor-bed condition the required volume of propellent. When this is not the case, however, and the active powder may be only sparingly sorbent of the propellent, a further propellent carrier medium is included in the aerosol mixture. A number of carriers which we have found to possess the desired sonption qualities include materials such as amorphous silica, crystalline silicates, and even metal such as aluminum powder.

The powder mixtures which may be dispensed by the present system includes as previously mentioned a wide variety. Essential for achieving a compatible system, however, there are certain characteristics required. Pri

marily, the powder composition must be capable of bold ing in an absorbed or adsorbed state all of the liquefied propellent necessary to dispense the container charge. The particle or mesh size of the powder imposes no strict limitation .on the operability of the system except as imposed by the aerosol container valve structure. In this respect, we have found that a desirable powder size is less than about 30 'mesh, and usually less than 100 mesh.

Also, in that the aerosol composition as contained will constitute a three-phase system, the powder must be insoluble in the liquid propellent employed. These propellents, broadly speaking, include hydrocarbons, fluorocarbons, and other gases liquefiable at ambient temperature' Some specific propellents include liquefied carbon dioxide, liquefied C to C hydrocarbons, sulfur dioxide, trichloromonofluoromethane (Ucon ll), monochlorodifluoromethane (Ucon 22), azeotropes of dichlorodifluoromethane and difluoroethane.

The preferred propellent employed in the prevent novel system may be one of those fluids normally associated with aerosol devices or a mixture of any of said fluids. In order to function properly, the propellent must have a relatively low boiling point as to be vaporizable from the sorbent powder upon activation of the container valve. Examples of propellents which are preferred for the purpose of this invention are dichlorodifiuoromethane (Ucon l2) and dichlorotetrafluoroethane (Ucon 114).

For the ordinary metallic aerosol container, the internal pressure head caused by vaporization of the propellent is generally about to 70 pounds per square inch gauge. For heavier containers, however, which are able to withstand greater pressures, lower boiling propellents may be used. We have found that when Ucon 12 is the propellent, a container vapor pressure of about 70 p.s.i.g. at 70 F. is to be expected. When a lesser pressure is desired, a preferred mixture of propellents such as Ucon 11 or Ucon 114 with Ucon 12 will lower the pressure generally in proportion to the amount of said propellents in the mixture.

When the propellent is not sorbed entirely on or into the active powder, an inactive propellent-sorbent carrier or secondary powder may be added tothe mixture. This latter may be an entirely inactive ingredient in the powder composition and should, therefore, be held to a minimum amount so as not to reduce the effectiveness of the overall system. Where the active ingredient of the composition is only slightly, if at all, sorbent of the propellent, the secondary powder will hold the entire propellent charge.

Several inactive carrier materials have been found to effectively retain substantial quantities of the propellent exposed surface areas in terms of square meters per gram.

As noted in the table, the powdered Cabosil (amorphous silica) will absorb up to about 85 to 90 percent of Ucon 12 before the inversion is reached when the powder is converted from the free-flowing state and commences to cake. Similarly, with silica No. 22, about 25 percent propellent will be absorbed before 'caking sets in. Thus, it may be seen that'for any particular self-propelled aerosol system,

the inactive or carrier powder may be chosen to supplement the function of the active ingredient. a

The following examples will serve to illustrate the dis closed self-propelled system when embodied in particular powder mixtures.

4 TABLE 1 Characteristics Exhibited by Various Powders in the Sorption of Ucon 12 at 70 F. and 70 p.s.z'.g.

Percentage by Weight of Liquid Adsorbed Before Powder Commences to Cake Powder A test aerosol system was made up containing as the active ingredient a major portion of Eveready Rose and Floral Dust, an insecticidal powder. A fiuidizing agent, Microcel B (calcium silicate) was intermixed with the active powder, said agent being present in an amount of about 5 percent by weight of the active powder. Into this homogeneous powder mixture, there was injected about 10 percent by Weight of liquid Ucon l2.

A series of tests were made in a manner similar to that described above; in these tests, varying quantities of the charge were ejected from a container after which the residue remaining in the container was analyzed to determine the relative proportions of powder to propellent. It was found in each instance that the powder remaining contained an amount of propel-lent approximately proportional to the initial loading ratio. That is, if the powder originally contained about 10% by weight of Ucon 12, the residue also contained about 10% by weight of the gas. These results are readily illustrated by reference to Table II and verify the fact that the propellent was actually sorbed by the powder charge, thereby providing the powder with self-propelling characteristics.

The self-propelled powders contemplated by the present invention may be delivered from many aerosolatype containers now known to the art. These containers are normally operated by a push-button actuated valve for releasing the container contents in a fluid stream. 'Norrnally the container charge is inserted through an opening in the upper end which also accommodates the valve.

TABLE II V Demonstration of Self-Propelling Character of Powder Final Load of Residue Product,

Initial percent Load (p cent Eveready Rose and Floral 90 91 Q2 90 gust (with 5% Microccl Ucon 12 Propellcnt 1o 7 1o 9 s 10 Ingredient Test 1 Test 2 Test 3 Test 4 When a self-propelled powder'of the type presently described is the. charge, there are several methods for filling a container. In a preferred method, a predetermined amount of the powder material is metered into the container. Thereafter, a predetermined amount of the liquid propellent is added, under pressure and/or in a chilled condition, the latter as previously described being in an amount as to be readily adsorbed or absorbed into the powder whether the latter be an active ingredient in thecharge or merely a carrier agent, This filling operation may be carried out at a lowered temperature thereby maintaining the propellent in a liquid condition and preventing. any substantial vaporization prior to the container being sealed.

An alternate method for charging a container consists of first adding the powder material to the container and thence injecting the propellent in the form of a gel consisting of the liquid propellent together with a suitable gelling agent. The latter may be readily added to the powder charge where, upon being agitated, it will form the desired self-propelled container charge. In either instance, it is beneficial to permit the composition to stand for a period of time in order that the propellent may become more thoroughly dispersed throughout the powder charge.

From the foregoing description, it is readily seen that the novel self-propelled powder aerosol system possesses many advantages. The fields of operation which 'had previously required a completely dry powder spray may now employ the present system without fear of contamination or detriment due to the presence of undesirable liquids. Also, it has been shown that efiiciencies of from 90 to 98% are realized so that the maximum benefit of the dispensed dust is achieved.

Further illustrative of the invention, self-propelled mixtures were made using the following compositions.

Agricultural dust: Weight, percent Eveready Rose Dust (with 5 wt. percent Microcel B) 90 Percent Malthion (O-O-dimethyl dithiophosphate of diethyl mercaptosuccinate) 5.00 Coptan (N trichloromethylmercapto- 4-cyclohexene-1 Z-dicarboximide) 7.5 Dinitro-1-(methyl heptyl) phenyl CIO tonate a 0.90 Other nitrogen derivatives chiefly dinitro (1-methyl heptyl) pheno1 0.10 Sulfur (93% minimum through 324 mesh) 15.00 Typical diluents (such as tales, pyrohyllites, diatomaceous earths, surfactants) 71.50 Ucon 12 Total 100 Medicated powder (foot powder) Talc N0. 7 87.55 Zinc stearate 1.75 Dichlorophene 0.70 Ucon propellent (12/11 mixture 50/50) 10.00

Total 100.00 Insecticide powder Lnaphthol-N-methyl carbamate 90 Ucon propellent (12/11 mixture 50/50) 10 Total 100 It has been found that iso-butane may be employed as the propellent in place of the Ucon material. In such an instance, iso-butane may be added in quantities about half that required by the Ucon propellents. Also among the successfully tried combinations, we have found that a powdered aluminum spray may be delivered against a surface to be coated in a stream of sulfur dioxide gas.

It is to be understood that certain improvements and modifications may be made in the invention by one skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

1. A three-phase self-propelling aerosol system for ejecting a substantially liquid-free stream of an active powder from a pressurized container therefor, which system comprises a free-flowing powdered composition to be ejected from the container, at least one component of said composition being particles of a liquid propellentsorbent material, and a vaporizable liquid propellent, a portion of which propellent is held in said sorbent material under the vapor pressure of said propellent normally existing within the container at the ambient temperature; said propellent being vaporizable by reducing the pressure normally existing within the container.

2. A three-phase self-propelling aerosol system for delivering a substantially liquid-free stream of an active powder from a pressurized container therefor, which system comprises a free-flowing powdered composition including, the active powder ingredient to be delivered, said active ingredient being only sparingly soluble in a vaporizable propellent, a second ingredient of said con1- position being highly sorbent of the vaporizable propellent, and the vaporizable propellent maintained in a sorbed condition by said powder composition under the vapor pressure of said propellent normally existing in the container at the ambient temperature, said propellent being present in the composition in sufficient amount to discharge substantially all of the active powder from the container.

3. A three-phase self-propelling aerosol system for ejecting substantially liquid-free stream of an active powder from a pressurized container therefor, which system comprises a free-flowing powdered composition to be ejected from the container, at least one component of said composition being particles of a liquid propellentsorbent material, and a vaporizable propellent selected from the group consisting of a fluorocarbon, a C to C hydrocarbon, carbon dioxide, and sulfur dioxide, a portion of which propellent is held in said sorbent material under the vapor pressure of said propellent normally existing within the container at the ambient temperature; said propellent being vaporizable by reducing the pressure normally existing within the container, and the proportion of said propellent to said powdered composition being such that said powdered composition remains freeflowing at all times.

4. The three-phase self-propelling aerosol system defined in claim 3 wherein the vaporizable propellent is trichloromonofluoromethane.

5. The three-phase self-propelling aerosol system defined in claim 3 wherein the vaporizable propellent is dichlorodifluoromethane.

6. The three-phase self-propelling aerosol system defined in claim 3 wherein the vaporizable propellent is monochlorodifluoromethane.

7. The three-phase self-propelling aerosol system defined in claim 3 wherein the vaporizable propellent is dichlorotetrafluoroethane.

References Cited in the file of this patent UNITED STATES PATENTS 2,954,935 Stearns et a1. Oct. 4, 1960 

1. A THREE-PHASE SELF-PROPELLING AEROSOL SYSTEM FOR EJECTING A SUBSTANTIALLY LIQUID-FREE STREAM OF AN ACTIVE POWDER FROM A PRESSURIZED CONTAINER THEREFOR, WHICH SYSTEM COMPRISES A FREE-FLOWING POWDERED COMPOSITION OF BE EJECTED FROM THE CONTAINER, AT LEAST ONE COMPONENT OF SAID COMPOSITION BEING PARTICLES OF A LIQUID PROPELLENTSORBENT MATERIAL, AND A VAPORIZABLE LIQUID PROPELLENT, A PORTION OF WHICH PROPELLENT IS HELD IN SAID SORBENT MATERIAL UNDER THE VAPOR PRESSURE OF SAID PROPELLENT NORMALLY EXISTING WITHIN THE CONTAINER AT THE AMBIENT TEMPERATURE; SAID PROPELLENT BEING VAPORIZABLE BY REDUCING THE PRESSURE NORMALLY EXISTING WITHIN THE CONTAINER. 